Heat exchanger using corrugated sheets

ABSTRACT

In an MVR evaporator, a heat exchanger core comprises several condensing units. Each unit comprises front and back corrugated sheets, arranged trough-to-trough. The units are arranged side-by-side, in peak-to-trough configuration, creating sinuous passageways between the units. Steam is fed into the units through port-pipes, and the units are physically supported via the port-pipes from steam manifolds.

This invention relates to heat exchangers, and to a cost-effectivemanner of construction thereof.

BACKGROUND TO THE INVENTION

The invention will be described herein mainly as it applies toevaporators. Evaporators are used in the treatment of industrialwastewaters, in that water is evaporated from the in-stream ofwastewater, thereby concentrating the contaminant in the final-waterout-stream. Evaporators are used when the savings in disposal costs morethan outweigh the costs of evaporation.

The invention is especially applicable to mechanical vapourrecompression (MVR) evaporators. Typically, in an MVR evaporator, waterand steam are present together in a state of pressure-temperatureequilibrium, at a pressure below atmospheric, in a vacuum chamber of acontainer vessel. Steam is extracted from the vacuum chamber, and iscompressed in such manner that the mechanical energy of compressionserves to raise the temperature, as well as the pressure, of the steam.The now-hotter steam passes through a condenser, in which it iscondensed into liquid water. The condensate is collected and conveyedaway.

The liquid water from the vacuum chamber serves as the coolant in thecondenser, i.e as the coolant that is used to condense the (hot,compressed) steam. The coolant is, of course, heated by its passagethrough the condenser, and some of the liquid water turns into steam. Infact, in equilibrium, the liquid water coolant, as it passes through thecondenser, turns into steam at the same rate at which steam is extractedfrom the vacuum chamber to be compressed.

An MVR evaporator typically is used in the cleanup of wastewater fromindustrial processes. Depending upon the temperature at which thewastewater is received, the wastewater might have to be pre-heated, butbasically, the MVR evaporator requires the the energy input (i.e theenergy needed to operate the evaporator) be only in the form ofmechanical energy. That is to say, the steam is heated by beingcompressed, rather than by direct heating.

The MVR process is, or can be, efficient, easy to control, andeconomical. The collected condensate is basically distilled water, aby-product which can be useful in various industrial processes.

A component of the MVR evaporator is the condenser. Here, heat isextracted from the compressed and heated steam at a sufficient rate tocondense the steam. The steam is only a few degrees hotter than thecoolant liquid water. The heat transfer relies on utilizing the latentheat of water, rather than on utilizing a large temperaturedifferential. As such, the heat exchanger (HE) that is the condensershould be thermally efficient. Also, the HE should be mechanicallyrobust, in that the HE needs to be designed to handle through-flows offluids at higher rates than is usual in other traditional HE designs.Also, the HE should be easy to clean, because scaling can be a problem.

The design of HE that is the subject of this specification is aimed atcombining those desiderata in a cost effective manner.

LIST OF THE DRAWINGS

The technology will now be further described with reference to theaccompanying drawings, in which:

FIG. 1 is a sectioned side elevation of a condensing unit of a HE.

FIG. 1 a is a (diagrammatic) end elevation of the condensing unit.

FIG. 2 is a pictorial view, partly cut away, of the condensing unit ofFIG. 1.

FIG. 3 is a diagram showing a HE that incorporates some condensingunits. The HE is shown incorporated into an MVR evaporator.

FIG. 4 is a sectioned side elevation of part of the condensing unitshown in FIG. 3, with some associated components.

FIG. 5 is a pictorial diagrammatic view of some of the components of theMVR evaporator of FIG. 3

FIG. 6 is a diagram of a pair of condensing units, illustrating some ofthe nomenclature used herein.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

In FIGS. 1, 1 a, 2, a heat transfer unit—in this case a condensing unit20—is made up from front and back sheets 23F, 23B of corrugatedmaterial. In FIG. 1, the front sheet 23F has been removed. Thecorrugated sheets 23F, 23B are attached together, trough-to-trough, thetroughs being held a small distance apart by spacer-strips 25. Fasteners27 clamp the troughs of the two sheets together, onto the spacer-strips25. The fasteners can be bolts, rivets, etc, as appropriate.

It is emphasized that the troughs of the corrugated sheets 23F, 23B donot actually make touching contact with each other, being held adistance D1 apart (FIG. 6) by the spacer-strips 25. Thus, in the areasbetween the spacer-strips 25, there is open space between the troughs,through which fluids can travel (i.e travel downwards) between thecorrugated sheets.

Top and bottom of the sheets 23F, 23B, channel-strips 28 sealingly closeoff the longitudinal edges of the sheets. In use, the pressure insidethe unit 20 is higher than the pressure outside, and the designersshould see to it that the channel-strips 28 remain firmly attached tothe sheets, despite the pressure differential.

At the left and right ends of the condensing unit 20, the space betweenthe corrugated sheets 23F, 23B is filled with respective masses 29L, 29Rof a sealant-filler. In FIG. 2, the lines 30 indicate the distance towhich the sealant-filler penetrates into the spaces between thecorrugated sheets. FIG. 1 also shows the extent to which the massespenetrate into the interior space between the sheets.

Embedded in the sealant mass 29L are two ports, the upper 32 being asteam-inlet port, and the lower 34 being a water-outlet port. The portscomprise respective short lengths of metal or plastic pipe. Theport-pipes 32, 34 communicate with the interior space between thecorrugated sheets. Apart from the ports, the interior space iscompletely sealed.

FIG. 3 shows a core of condensing units 20 that together make up the HE36. It will be observed that, in FIG. 3, while the front and backcorrugated sheets 23F, 23B of the individual condensing units 20 areassembled trough-to-trough, the units 20 are assembled to each other inpeak-to-trough configuration. That is to say, the corrugations betweenadjacent units are—preferably exactly—out of phase with each other.

The individual condensing units are spaced from their adjacentneighbouring units, and it will be observed, again from FIG. 3, thatassembling the condensing units 20 in peak-to-trough configurationcreates sinuous passageways 38 between adjacent condensing units. Thesepassageways, though sinuous, are of uniform horizontal width (dimensionD2 in FIG. 6) along their vertical lengths.

Preferably, the corrugated sheets are regular, i.e all the peaks arepitched the same distances apart, and all the peaks and troughs are ofthe same amplitude. Preferably also, all the sheets used in the HE areof the same profile of regular corrugation. When that is so, the unitsdo not need to be specially matched and aligned.

Each condensing unit 20 is a rigid structure, in itself. Preferably, theinlet and outlet ports of the unit are duplicated at the left and rightends of the condensing unit (as may be seen in FIG. 2). Then, thecondensing unit can very readily support itself, simply as a result ofthe port-pipes 32, 34 being inserted into suitable apertures orpipe-holes located at the ends of the unit 20. Furthermore, the wholecore of several condensing units can be supported on suitably-placedrespective holes.

It is not essential that the condensing units 20 be supported on theirport-pipes, although that is the preferred manner of support. Thecondensing units are easy to support, in that the units have manydownwards-facing surfaces, which can engage, and rest on, e.g pegscarried in a suitable unit mounting means.

As will be understood from FIGS. 3, 4, 5, the condensing units 20 aresupported on the pipe-holes 42 formed in left and rightsteam-inlet-manifolds 40L, 40R. Mechanically, the manifolds support allthe condensing units, and hold the units in their correct relativepositions. Thus, the steam-inlet manifolds do double duty: they alsocollect steam and feed it into the ports 32, and thence into theinterior spaces of all the condensing units. Steam enters thesteam-inlet-manifold 40L via a manifold inlet-pipe 41.

Left and right water-outlet-manifolds 43L, 43R also provide mechanicalsupport from the condensing units 20, and serve to collect and conveyliquid water out of the units. In FIGS. 3, 5, each condensing unit isprovided with six steam-inlet ports 32 and two water-outlet ports 34(steam occupying much more volume than water, of course).

FIG. 4 illustrates how the upper and lower manifolds 40L, 43L engagewith the several condensing units 20, at the left end of the HE 36. Thepipe-holes 42 are provided with seals 44, which seal the port-pipes 32,34 with respect to the manifolds.

Once the several condensing units 20 have been assembled between themanifolds 40L, 43L and 40R, 43R, the manifolds are fastened to a cover45. The cover 45 is formed from sheet metal, and is arranged to rest ona floor or platform 47 inside a chamber 49. The cover holds themanifolds in place, and the manifolds in turn brace the cover into itsconfiguration as shown.

The cover 45 is basically open at the ends, and underneath, and is notairtight or watertight. A bracket 50 braces the sides of the cover 45,and holds them correctly spaced over its length. Of course, the designershould see to it that such brackets, between the sides of the cover 45,do not interfere with the HE core.

The cover 45 as shown is made of sheet material; however, the cover canalternatively be formed as a framework or skeleton. The floor 47 of thechamber 49 is open, i.e water can pass downwards, from the HE, throughthe floor.

The cover 45 is equipped with a number of spray-heads 52, suitablypitched in the roof portion of the cover. Water from the spray-headspasses down the sinuous passageways 38 between the condensing units 20.Thus, water from the spray-heads 52 makes vigorous contact with theoutside surfaces of the corrugated sheets 23 of the condensing units.

As a result of the vigorous contact, heat is transferred from the steaminside the condensing units 20 into the down-flowing water.Consequently, the steam inside the units 20 condenses, and the water inthe sinuous passageways 38 evaporates.

Generally, the designers will prefer that the water does not actuallyboil, when in contact with the corrugated sheets. Formation of physicalbubbles on the metal surfaces would adversely affect heat transferrates. Preferably, therefore, the water passing through the passageways38 is collected and pumped back and rapidly re-circulated through thepassageways, to keep bubble-formation to a minimum. Preferably, thecirculation rate of the liquid water (as generated by the water-pump58), measured as a flowrate of F kg/min, should be about five, or more,times the rate in kg/min at which the water evaporates.

FIG. 3 contains some exemplary values of the magnitudes of the pressureand temperature of the water as it passes through the MVR evaporator.

Contaminated water enters the evaporator through the entry-port 56. Thiswater is typically received at a temperature of 65° C. (If the water iscold, it can be economical to pre-heat the water to this temperature.)The incoming dirty water is pumped (by water-pump 58) to the spray-heads52. The sprayed water passes down through the sinuous passageways 38between the condensing units 20, picking up heat from the steam insidethe units.

Much of the falling water remains as liquid, and falls into the pool 60of water resting on the bottom of the chamber 49. But some of thefalling water evaporates, and passes into the upper areas of the chamber49. The still-contaminated water collected in the pool is re-pumped backto the spray-heads 52, whereby the dirty water is circulated andre-circulated through the HE core, some of its water content beingevaporated each pass.

The contaminant in the water does not evaporate. (The operators shouldbe sure to keep the temperature inside the chamber below the temperatureat which the contaminants might be volatile.) Therefore, the contaminantconcentration in the water in the pool 60 is considerably stronger thanin the incoming water in the entry-port 56.

The water in the pool 60 is discharged from the evaporator, through theconcentrate-discharge port 65, as concentratedly-contaminated water, thedisposal of which is more economical than the direct dispoal of thedilutely-contaminated water entering through the dirty-water entry-port56.

Typically, the pressure inside the chamber 49 is maintained at about 0.3bar (atmospheres), i.e well below atmospheric pressure. At this (low)pressure, water boils at 70° C. The steam inside the chamber 49, at apressure of 0.3 bar and at a temperature that can be equated to 70° C.,is drawn into a steam-blower 63. Here, its pressure is increased—in thisexample to about 0.6 bar. The compression produces an increase intemperature, in the steam—to about 80° C. in this example.

This steam, which is now at 80° C. and 0.6 bar, passes into thesteam-inlet manifolds 40, and thence into the steam inlet ports 32 ofthe condensing units 20. Inside the condensing units 20, the steamcondenses, and drips down into the lower regions of the units. Thecondensate water is drawn through the water-outlet ports 34, thewater-outlet manifolds 43, and the manifold outlet-pipe 66, and isdischarged from the evaporator via the condensate-discharge port 67.

The condensate water in the condensate-discharge port 67 is still hot,and its heat can be utilized for example to pre-heat the incoming dirtywater (e.g in a suitable HE apparatus). The condensate water is more orless pure H2O, in which state it can be useful in many industrialprocesses.

As mentioned, it can be advantageous to thoroughly drench the HE corewith the contaminated liquid water, and to circulate and recirculate thedirty water very vigorously through the HE. This vigorous drenchingaction of the water can be mechanically demanding on the structure ofthe HE.

Therefore, the structure of the core needs to be robust. In the designsas depicted herein, the individual condensing units, constructed asdescribed, are remarkably strong and rigid, in themselves. That beingso, all that is needed by way of mechanical support for the units is,basically, something for them to rest on; as a result, the supports arenot required to contribute much by way of rigid structural support.

Another factor the designers should have in mind is that the spacesbetween the individual condensing units should be accurately maintained.It would not do for the sinuous passageway behind the unit to be widerthan the one in front of the unit. The condensing units should besupported in such manner as to render the spacing between them uniform.

Another factor in the design of the support for the units is that, whenthe HE is dismantled (e.g for cleaning or de-scaling), the design shouldbe such that the technicians can reassemble the units in exactly thesame mutual spacing relationship with each other.

The support for the units as depicted herein, in which the units aresupported from their port-pipe, and the port-pipes are simply insertedinto holes in the manifolds, can provide the required ease of assemblyand disassembly, and the required accuracy of positioning of the units.

If the several individual condensing units were so designed that theyhad to be, for example, bolted together for assembly, that would not bepreferred, when compared with the illustrated designs, not least becauseremoving and replacing many (threaded) fasteners is time consuming andlabour intensive.

By contrast, the condensing units 20 do not have to be (and cannot be)dismantled, e.g for cleaning the interiors thereof. The more elaborateand non-dismantlable construction of the units, with theirspacer-strips, many fasteners, and their filler-sealant masses, isacceptable because that construction can be done, and finished, on anin-factory basis.

The corrugated sheet-metal, from which the front and back walls of thecondensing units are formed, serves as a thermal partition. The wallskeep the fluids apart, but permit heat to pass between the fluids. Assuch, the walls should be of thin metal, for efficient heat transfer. Athickness of between about 0.3 and 1.0 millimetre is preferred. Eventhough the walls are thin, the shape and configuration of the units, asdescribed, gives them sufficient stiffness and strength for the units tobe highly suitable for performing the described functions.

Typically, the designers will prefer to use stainless steel for themetal components of the HE, as the presence of hot contaminated watercan exacerbate corrosion problems.

Besides being very suitable for use in MVR evaporators, the heatexchanger as described herein is also suitable for use in otherapplications, especially where the fluids between which heat isexchanged both pass through gaseous and liquid phases.

The described HE is also efficient enough to be very suitable for usewhen the available temperature differentials are only a few degrees.Thus, the HE is very suitable for use with low-grade heat.

The sinuous passageways are effective in ensuring good heat transfer, inthat movement of the water down the sinuous passageways serves to mixand stir the water very thoroughly, whereby any temperature differencesand gradients, measured on a drop-to-drop basis, in the falling water,are quickly dissipated. Also, the falling water impinges vigorously themetal surfaces many times during travel through the passageways, whichassists in heat transfer.

Regarding the seals around the periphery of the corrugated sheets 23,i.e the seals that define the perimeter of the interior space createdbetween the sheets: of course, preferably, the seals should not leak.However, expensive leakproofing is not required, in that a small leakageis of little consequence, in that the leakage would be outwards, sincethe pressure inside the unit is higher than the pressure outside, sothere would just be a leakage of steam and/or condensed water back intothe chamber, and the condensate likely would not be subjected tocontamination. In any case, it is generally an easy matter to make theseal complete.

The masses 29 of filler-sealant can be of injectable expanding foam,which sets solid. The port-pipes 32, 34 are first positioned between thefront and back sheets, and then the foam is injected around them. Thechannel-strips 28 also are easy to seal, again simply being filled withexpandable foam as they are assembled. The seals as described are robustenough to support fluid pressure inside the interior space 35 of theunit. The sealed condensing unit is permanent, in the sense that it isnot dismantlable.

It is a simple matter to take the HE out of the chamber, for cleaningand de-scaling. The cover 45 is arranged simply to slide out of thechamber 49, over the open platform 47, with very little dismantlingbeing required before that can be done. With the HE outside the chamber,it is a simple matter to separate the manifolds from the cover, and thenthe manifolds can simply be pulled off the left and right ends of the HEcore. The individual condensing units can then be handled separately,for cleaning.

FIG. 6 shows two of the heat transfer units in their side-by-sidepeak-to-trough configuration, and illustrates some of the nomenclatureused herein.

A peak viewed from one side of the sheet is, of course, a trough whenviewed from the other side of the sheet. Herein, a peak is a peak whenviewed from the outside of the heat-transfer (condensing) unit. Thus, inFIG. 1 a, etc, the corrugated sheets are fastened together in atrough-to-trough configuration.

The sinuous passageway 38 preferably is sinuous enough that there is nostraight path through which water could fall. In passing downwards,preferably the steam/water traverses, and changes direction at, at leastsix peaks—i.e three on each side of the passageway. In FIG. 3, forexample, the falling water encounters (and changes direction at)fourteen peaks.

In FIG. 6, a path-line 69 traces the shortest path that fluid can takein passing through the passageway. The path-line 69 passes from a peakP1-F-U1 of the sheet F-U1 to a peak P1-B-U2 of the sheet B-U2, and thento a peak P2-F-U1 of the sheet F-U1, and then to a peak P2-B-U2 of thesheet B-U2, and so on. The portion of the path-line 69 joining peakP1-F-U1 to peak P1-B-U2 lies at an angle A to the portion of thepath-line joining peak P1-B-U2 to peak P2-F-U1. Preferably, the angle Ais no more than about 150 degrees.

The sinuousness of the passageway 38 may be expressed in another way.The peak-to-trough height of the corrugations, being PTH centimetres,preferably is larger than the distance D2 between the sheets F-U1 andB-U2, whereby the peaks of sheet F-U1 overlap the peaks of the sheetB-U2. This being so, steam/water cannot follow a straight path throughthe passageway. More preferably, the spacing D2 is about one-half ofPTH.

The apparatuses as depicted include sheet-spacers, being thespacer-strips 25 as described, which hold the front and back sheets ofthe respective condensing units the distance D1 apart. Equally, thedepicted apparatuses include unit-spacers, which hold the adjacent unitsthe distance D2 apart. The unit-spacers are, in the drawings, providedby the pipe-holes of the manifolds, which receive the respectiveport-pipes of the several condensing units. The pipe-holes in themanifolds are so positioned, relative to each other, that the severalunits are thereby held firmly in the required side-by-side,peak-to-trough configuration.

The HE as shown is arranged horizontally, and that is preferred forconvenience. Alternatively, the HE can be arranged to operate in otherorientations.

Some of the components and features in the drawings have been givennumerals with letter suffixes, which indicate front, back, etc, versionsof the components. The numeral without the suffix is used herein toindicate the component generically.

Terms of orientation, such as “above”, down”, “left”, and the like, whenused herein are intended to be construed as follows. When the terms areapplied to an apparatus, that apparatus is distinguished by the terms oforientation only if there is not one orientation into which theapparatus, or an image of the apparatus, could be placed, in which theterms could be applied consistently.

The scope of the patent protection sought herein is defined by theaccompanying claims. The apparatuses and procedures shown in theaccompanying drawings and described herein are examples.

The numerals used in the drawings are:

-   20 condensing unit-   23F,B front and back corrugated sheets-   25 spacer-strips-   27 fasteners-   28 top and bottom channel-strips-   29L,R left and right masses of filler-sealant-   30 extent of sealant masses-   32 upper port=steam-inlet port-pipe-   34 lower port=water-outlet port-pipe-   35 sealed interior space of 20-   36 heat exchanger (HE) core-   38 sinuous passageways between condensing units 20-   40L,R left and right steam-inlet manifolds-   41 steam manifold inlet-pipe-   42 pipe-holes-   43L,R left and right water-outlet manifolds-   44 seals for 42-   45 cover-   47 floor or platform of 49-   49 chamber-   50 bracket (brace) for 45-   52 spray-heads-   56 dirty water entry-port-   58 water pump-   60 pool of water in 49-   63 steam-blower-   65 concentrate-discharge port-   66 manifold condensate outlet-pipe-   67 condensate-discharge port-   69 shortest path-line through 38

1. Heat exchanger apparatus, wherein: the apparatus includes severalheat transfer units, and in respect of each unit: the unit includesfront and back corrugated sheets, which are fastened together in atrough-to-trough configuration; the unit includes sheet-spacers, and thesheet-spacers hold adjacent corrugation troughs of the front and backcorrugated sheets in a spaced-apart relationship, a distance D1 apart;the unit includes peripheral seals, which straddle sealingly between thespaced-apart sheets, thereby creating a sealed and enclosed interiorspace between the sheets and between the seals; the unit includes inletand outlet ports, through which fluid can be introduced into, anddischarged from, the interior space; the several heat-transfer units arearranged side by side, and form a core of the heat exchanger apparatus;the apparatus includes a support, in which the several units of the coreare mounted, and the support is structured to so mount adjacentheat-transfer units, in the core, that: the front sheet F-U1 of one ofthe heat transfer units U1 faces the back sheet B-U2 of the nextadjacent unit U2; the said front and back sheets F-U1 and B-U2 face eachother in a peak-to-trough configuration; the support includesunit-spacers, and the unit-spacers hold the units U1 and U2 inspaced-apart relationship, a distance D2 apart; the distance D2 betweenthe sheets F-U1 and B-U2 is large enough to create and define apassageway between those sheets, which is large enough to enable fluidto pass between those sheets; the distance D2 is small enough thatfluid, in passing through the passageway between the units U1 and U2,and in encountering the peaks and troughs of the sheets F-U1 and B-U2,is forced by such encounters to undergo respective substantial changesof direction; whereby the passageway created between adjacentheat-transfer units can be characterized as sinuous.
 2. As in claim 1,wherein the arrangement of the apparatus is such that fluid passingthrough the sinuous passageway encounters at least three peaks each ofthe corrugated sheets F-U1 and B-U2, being at least six peaks inaggregate.
 3. As in claim 1, wherein: in respect of a path-line thattraces the shortest path that fluid can take in passing through thepassageway; the path-line passes from a peak P1-F-U1 of the sheet F-U1to a peak P1-B-U2 of the sheet B-U2, and then to a peak P2-F-U1 of thesheet F-U1, and then to a peak P2-B-U2 of the sheet B-U2, and so on; theportion of the path-line joining peak P1-F-U1 to peak P1-B-U2 lies at anangle A to the portion of the path-line joining peak P1-B-U2 to peakP2-F-U1; the angle A is no more than about 150 degrees.
 4. As in claim1, wherein: the corrugations of sheet F-U1 are of the same pitch and thesame peak-to-trough height, being PTH centimetres, as the corrugationsof sheet B-U2; the distance D2 between the sheets F-U1 and B-U2 issmaller than the height PTH, whereby the peaks of sheet F-U1 overlap thepeaks of the sheet B-U2; and preferably D2 is about one-half of PTH. 5.As in claim 1, wherein the sheet-spacers that hold the sheets thedistance D1 apart in the unit include spacer-strips of thickness D1,fasteners go through them, at the troughs, clamp sheets ontospacer-strips.
 6. As in claim 1, wherein: the peripheral seals includeleft and right masses of filler-sealant; and each mass straddles betweenthe front and back sheets.
 8. As in claim 1, wherein the inlet andoutlet ports of the unit comprise respective inlet and outletport-pipes.
 9. As in claim 8, wherein the port-pipes are embedded in thefiller-sealant.
 10. As in claim 1, wherein: the apparatus includes aninlet manifold; the inlet manifold is formed with pipe-holes, the wallsof which are suitably sized to receive the port-pipes of the severalunits; the walls of the pipe-holes in the inlet manifold are sopositioned relatively that, when the port-pipes of the several heattransfer units are received therein, the walls of the pipe-holesconstrain the port-pipes of one unit against movement towards and awayfrom the other units; whereby the walls of the pipe-holes of the inletmanifold serve as the said unit-spacers.
 11. As in claim 10, wherein thewalls of the pipe-holes in the inlet-manifold are so positionedrelatively as to support the several units, the port-pipes of which arereceived therein, in the said peak-to-trough configuration.
 12. As inclaim 1, wherein: the HE apparatus is a component of an evaporator; inthe evaporator, incoming water containing a dissolved contaminant at adilute contamination is evaporated, whereby, in the outgoing finalwater, the contaminant is more concentrated; the arrangement of theevaporator is such that, in use, steam entering the inlet ports of theunits is condensed upon passing through the units, and water passingthrough the passageways is evaporated.
 12. As in claim 1, wherein: theevaporator is an MVR evaporator; the evaporator includes a chamber, inrespect of which: the contaminated water is circulated through thesinuous passageways; steam is drawn, and compressed, and then fed intothe inlet ports of the heat transfer units.